In general, a combustion pressure sensor for detecting combustion pressure includes a tubular housing having an axial hole extending in the direction of an axis; a rodlike pressure transmission body inserted into the axial hole such that its front end portion is exposed to the outside; and a sensor element which outputs a signal on the basis of a pressure applied thereto from the pressure transmission body. The housing includes a main body portion which has, on its outer circumferential surface, a screw portion for screw engagement with a mounting hole of an internal combustion engine; and a cap member joined to a front end portion of the main body portion. When the combustion pressure sensor is attached to the mounting hole of the internal combustion engine, a press contact portion provided at a front end portion of the cap member is press-contacted with the internal combustion engine, whereby sealing is established between the internal combustion engine and the combustion pressure sensor.
Also, there has been known a technique in which the above-mentioned pressure transmission body is fixed to the housing via a flexible member which is diplaceable along the direction of the axis, whereby the pressure transmission body is made movable in relation to the housing in the direction of the axis, and pressure can be transmitted from the pressure transmission body to the sensor element (see, for example, Patent Document 1).